Method for controlling a holding force against, and limiting impact with travel limit positions

ABSTRACT

An actuator includes a motor operated by a controller through a pulse width modulation drive signal applied to a drive circuit that drives the motor. The actuator has an output shaft connected to a coupling structure for manipulating a device such as a variable geometry turbine (VGT) or an exhaust gas recirculation (EGR) valve. The device has a range of motion limited by first and second mechanical stops located at opposing low and high ends of the range. The controller learns the location of the mechanical stops during calibration. An external control unit transmits a desired position to the actuator. A protocol allows the external control unit to implicitly request a positioning mode by virtue of what value range the desired position falls into. The controller is configured to limit the drive signal to a non-harmful level when one of the positioning modes calls for pushing the device against one of the stops.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. Ser. No.11/928,718, filed Oct. 30, 2007, entitled “METHOD FOR CONTROLLING AHOLDING FORCE AGAINST, AND LIMITING IMPACT WITH TRAVEL LIMIT POSITIONS”.

TECHNICAL FIELD

This invention relates generally to a method for operating an actuator,and more particularly to a method for controlling a holding forceagainst travel limit positions.

BACKGROUND OF THE INVENTION

It is known to provide a so-called Smart Remote Actuator (SRA), which isan electro-mechanical device that is configured to actuate or manipulatean attached device, such as for example an engine feature like aposition of a variable geometry turbocharger (VGT) or a position of anexhaust gas recirculation (EGR) valve. In one construction, the SRAincludes a brushless direct current (BLDC) motor, whose rotor is coupledto a gear-train, which in turn is coupled to an output shaft. The outputshaft of the SRA is configured to be coupled by way of intermediatelinkage such as a second gear train or a lever-connecting rod-levercombination or the like to transfer the rotation of the output shaft toa desired movement of the manipulated device (e.g., rotation of an EGRvalve throughout its operating range). The SRA may include integratedrotary position detection hardware/software that is configured toprovide an indicated position of the actuator as feedback.

It is known to use an SRA in a VGT application. In this application, theactuator operates the VGT over a range of travel that avoids physicalcontact with the mechanical travel limits, except when those travellimits are deliberately contacted for the purpose of learning theirlocations. For this application, not contacting the travel limits wasacceptable. However, for other applications, such as an EGR valveapplication, the precision needed required that the mechanical travellimits sometimes be contacted, perhaps for indefinite periods of time. Aproblem with contacting the mechanical travel limits, especially forextended periods of time, is that the phase currents provided to themotor would overheat the motor and perhaps damage it. This is due inpart to the characteristics of the motor. In operation, when the rotoris rotating, a back electromagnetic force (BEMF) is produced which tendsto reduce the amount of current that flows through the coils for a givenapplied voltage. However, in a stall condition, as would exist whencontacting a travel limit, only the resistance of the coils themselves(generally low) impedes current flow, which can result in an excessivecurrent situation. It is this excessive current that producesundesirable amounts of heat—potentially damaging the motor and/orassociated packaging/components.

There is therefore a need for a method for controlling a holding forceagainst travel limit positions that minimizes or eliminates one or moreof the problems noted above.

SUMMARY OF THE INVENTION

The present invention provides a method of controlling the operation ofa motor-based actuator so as to achieve over-temperature protection whenthe actuator is causing the manipulated device to apply a force (“push”)against one of the mechanical stops (“travel limits”).

In accordance with an embodiment of this invention, a method ofoperating an automotive vehicle actuator is provided. The actuatorincludes a motor that is coupled to a manipulated device on theautomotive vehicle. The manipulated device is configured to travelthrough a range of motion and the range of motion limited at least atone end by a mechanical stop. The method includes the step ofdetermining that the actuator has received a command to push themanipulated device against the mechanical stop. The method also includesthe step of determining a drive signal to be applied to the motorcorresponding to a predetermined holding force of the manipulated deviceagainst the mechanical stop. The method further includes the step ofapplying the drive signal to the motor so the manipulated device pushesagainst the mechanical stop with the predetermined holding force afterreaching the mechanical stop.

In accordance with an embodiment of this invention, a method ofoperating an automotive vehicle actuator also includes the step ofdetermining that the actuator has received a command to push themanipulated device against the mechanical stop includes the steps ofreceiving a commanded device position that is beyond the mechanicalstop, and operating the actuator to move the manipulated device to aposition near the mechanical stop.

In accordance with an embodiment of this invention, an automotivevehicle actuator is provided. The actuator is configured to move amanipulated device on the automotive vehicle that is configured totravel through a range of motion. The range of motion is limited atleast at one end by a mechanical stop. The actuator includes a motor anda controller. The motor is coupled to the manipulated device. Thecontroller is configured to determine that the actuator has received acommand to push the manipulated device against the mechanical stop. Thecontroller also is configured to determine a drive signal to be appliedto the motor corresponding to a predetermined holding force of themanipulated device against the mechanical stop. The controller isfurther configured to apply the drive signal to the motor so themanipulated device pushes against the mechanical stop with thepredetermined holding force after reaching the mechanical stop.

The invention is directed to a method of operating an actuator having amotor where the actuator is coupled to a manipulated device, such as anEGR valve or the like. The manipulated device is configured to travelthrough a range of motion limited by first and second mechanical stopslocated at opposing low and high ends of such range. The method includesa number of steps. The first step involves determining an error signalas a difference between a commanded actuator position and a present(e.g., sensed) actuator position. Next, determining a candidate level ofa drive signal for driving the motor as a function of the determinederror signal and a predetermined control strategy. The final stepinvolves limiting the candidate level of the drive signal level so as tonot exceed a predetermined maximum level when a holding force limit flagis set. The predetermined maximum level corresponds to a predeterminedholding force of the manipulated device against one of the mechanicalstops. The limiting step restricts the current through the motor coilswhen “pushing” against a mechanical stop.

The method also provides a mechanism for an external control unit toencode in its desired position command to the actuator, a request forone of a plurality of positioning modes. This mechanism allows theactuator to distinguish between an external request to cause themanipulated device to push against one of mechanical stops, on the onehand, versus an external request to simply position the manipulateddevice at one of the mechanical without applying a force (“pushing”).

In another aspect of the present invention, a method of operating theactuator is provided that minimizes or eliminates excessive impact ofthe manipulated device against the mechanical stops due to rotationalinertia built up when responding to relatively large changes in thecommanded position that takes the manipulated device into the stop.

Other features of the method as well as a system are also presented.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example, withreference to the accompanying drawings:

FIG. 1 is a schematic and block diagram of a smart remote actuatorsystem having a holding force limit feature.

FIG. 2 is a diagram showing the range of travel of the actuator whenconnected to a manipulated device (load).

FIG. 3 is a flowchart diagram showing a method for controlling theactuator position or a holding force against travel limit positions.

FIG. 4 is a diagram showing the range of travel of the actuator in theregions near the stops.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference numerals are usedto identify identical components in the various views, FIG. 1 issimplified schematic and block diagram view of a system 10 that includesa smart remote actuator (SRA) 12 coupled to a load 14 configured to beactuated by SRA 12. In the illustrated embodiment, the load 14 includesa coupling structure 16 and a manipulated device 18. As described in theBackground, the manipulated device 18 may take the form a variablegeometry turbine (VGT), an exhaust gas recirculation (EGR) valve, or anyother device that has a range of travel 20 between and limited by afirst mechanical stop MSP₁ and a second mechanical stop MSP₂ where thefirst and second mechanical stops are located at opposing low and highends of such range of travel 20. The present invention will findparticular utility in those applications where it is desired or requiredthat the manipulated device (e.g., an EGR valve) not only contact one ofthe mechanical stops but also apply a holding force against themechanical stop (travel limit) as well. It is in these situations wherethe methodology of the present invention is effective at providingover-temperature protection to the SRA 12. It should be understood thatthe present invention is not limited to only two stop configurations,although this configuration will be the most common (i.e., it iscontemplated that the aspect of the invention involving limitation onthe holding force can be applied to just one stop as well). As shown inFIG. 1, the device 18 may assume a number of positions within the travelrange 20, designated by points P₀, P₁ and P₂.

In general terms, an external control unit 22 is configured to transmita desired position signal 24 to the SRA 12. The desired position signal24 is indicative of a desired position that the control unit wants themanipulated device 18 to assume within the travel range 20. In anautomotive vehicle application, the control unit 22 may be an electronicengine controller. The SRA 12 is configured to process the desiredposition signal 24, as more fully described below, and cause an outputshaft 26 thereof to rotate. Such rotation, which may be either clockwiseor counter-clockwise, is coupled through the coupling structure 16 toeffect movement of the device 18 toward the desired position, asindicated by signal 24. As known, the coupling structure 16 may comprisea gear, a gear train, movable bars or other mechanical linkagesappropriate for the target application to translate the movement of theoutput shaft 26 to a corresponding movement of the manipulated device18.

As to internal construction, the SRA 12 includes a controller 28, adrive circuit 30, a motor such as a brushless direct current (BLDC)motor 32 having a rotating rotor 34, a motor position sensor block 36, agear train 38 and a gear train position sensor 40.

The controller 28 is configured generally to execute preprogrammedinstructions (i.e., software) to control the operation of the SRA 12.Accordingly, the controller 28 may comprise conventional processingcapability configured to execute such preprogrammed instructions. Thecontroller 28 additionally includes both random access memory (RAM) 28 aand non-volatile memory such as read-only memory (ROM) 28 b or othertypes of programmable memory that can be modified during operation yetretain the stored information once power is removed. The controller 28is configured to include sufficient processing capability and resourcesto execute the control methodology described herein, as would beunderstood by one of ordinary skill in the art. The controller 28 alsoincludes a variety of input/output (I/O) connections suitable forreceiving inputs from various sensors and other inputs, as well as forproducing necessary outputs, as described herein.

The controller 28 is further configured to communicate with the externalcontrol unit 22. In one embodiment, the SRA 12, through appropriateconfiguration of the controller 28, includes functionality tocommunicate in a plurality of different formats through correspondingplurality of interfaces, for example as seen by reference to U.S. Pat.No. 6,864,788 entitled “ACTUATOR CONTROLLER FOR SELECTING ACOMMUNICATION LANGUAGE” issued to Crawford et al., owned by the commonassignee of the present invention and hereby incorporated by referencein its entirety. The SRA 12 may be configured to receive the desiredposition signal 24 via the following approaches: (1) in a digital formthat is transmitted in a serial fashion via a UART (UniversalAsynchronous Receiver Transmitter); (2) in a digital form transmittedover a CAN network (Controller Area Network); and (3) in the form of aduty cycle of a desired position pulse width modulated (PWM) signal. Inthe UART and CAN approaches, the digital information that represents thecommanded device position may have a value in the range of (0) to(1000). In the PWM approach, the duty-cycle range may vary in the rangebetween (50) and (950). According to the invention, as described ingreater detail below, some additional expansion of this range isprovided for to allow enhanced communication between the externalcontrol unit 22 and the SRA 12. As will be described in greater detailbelow, the desired position signal 24 may be used by the externalcontrol unit 24 to communicate a requested positioning mode to the SRA12—the positioning mode corresponding to how the manipulated device ispositioned throughout its range of motion, including how it contacts and“pushes” against mechanical stops. As described in greater detail below,the commanded device position (0-1000) drawn from the desired positionsignal 24 is subsequently mapped by the controller 24 to a commandedactuator position.

The UART and CAN approaches may be 2-way communication schemes, wherethe SRA 12 is configured to report back an indicated position of themanipulated device whenever it receives the desired position signal 24.The PWM approach, however, is contemplated to involve only one-waycommunication (i.e., the SRA 12 receives the signal 24 as an input only,with no reporting back of an indicated position of the actuator).

With continued reference to FIG. 1, the motor 32 may be a conventionalBLDC motor 32 having a rotor 34 coupled to a gear train 38. The sensorblock 36 may include three (3) Hall-Effect sensors arranged in aconventional manner to detect the position of the rotor, as it rotates,in six different steps. The gear train 38 may be a 2-stage gear train(e.g., the motor rotor/pinion gear is coupled to an idler gear which iscoupled to a sector gear having the output shaft 26). In this regard,the idler gear (not shown) may be configured to include a magnet (notshown) so that as the idler gear rotates, the magnet sweeps through anarc/range of motion. The sensor 40 may also be a Hall-Effect sensorarranged in space to detect the presence of the magnet. The overallcombination of the sensor 40 and the magnet in idler gear is such thatat approximately the center of the range of motion 20 of the manipulateddevice 18, the sensor 40 will detect the presence of the magnet andprovide a corresponding signal to the controller 28. The purpose of this“center of travel” detection functionality will be described in greaterdetail below.

In the illustrated embodiment, the drive circuit 30 is responsive to,preferably, a plurality of drive signals, collectively the drive signal42, for the timed production of respective phase currents 44 forenergizing/commutating the various phases of the motor 32, so as tocontrol the direction and speed of rotation of the rotor output 34. Thedrive circuit 30 may comprise conventional components (e.g., powertransistors, etc.) known to those of ordinary skill in the art for suchpurpose. The controller 28 may be configured to determine and generatesuch drive signals. The drive signal 42 may be a fixed frequency signalthat has a variable duty-cycle to define a motor pulse width modulation(MPWM) signal, for example, as seen by reference to U.S. Pat. No.7,053,583 entitled “BRUSHLESS DC MOTOR CONTROL” issued to Hazelton,owned by the common assignee of the present invention and herebyincorporated by reference herein in its entirety. It should beunderstood that the MPWM drive signal 42 involved in driving the motorphases is not the same as the desired position PWM signal which may beused as one form of the input desired position signal 24.

The objects of the present invention are two-fold. First, to provide amechanism to limit the holding force of the manipulated device againstthe stop. The second object is to minimize or eliminate excessive impactof the manipulated device with the mechanical stops, which if leftuncontrolled, may result in damage to the gear-train.

Before proceeding to a detailed description of a method for controllingthe holding force of the manipulated device against a mechanical stop,some additional background description will be set forth for greatercontext. Before the SRA 12 can be operated, the controller 28 needs toknow the location of the mechanical stops MSP₁ and MSP₂ along the rangeof travel 20. In this regard, the controller 28 is configured asfollows. If, upon power-up, the SRA 12 has no initial mechanical stoplearn history stored in its non-volatile memory, it is configured toautomatically perform a slow initial stop-learning sequence that will bereferred to as a “calibration”. The SRA 12 will, under the control ofthe controller 28, rotate its output shaft 26 and determine the locationsuch system defined end-stops (i.e., the mechanical stops MSP₁ andMSP₂). The initial time the controller 28 performs stop-learningsequence (“calibration”), the motion is deliberately slow and motioncontrolled such that a controlled windup in the various mechanisms(e.g., in the coupling structure 16) occurs. For example, if fast motionis employed, the inertia of the various mechanisms may result in asituation where the motor has rotated to a position “beyond” that of thereal, manipulated device (e.g., accounting for backlash, bending ofbars, if any, etc.) potentially resulting in a less accuratedetermination of the end-stop location.

If, on the other hand, a previous “calibration” has been performed andthus the controller 28 has available for use previously-stored stopvalues, it is configured to automatically perform a fast, subsequentstop-learning sequence.

FIG. 2 is a range-of-travel diagram for the SRA 12 connected to load 14,which will be used in describing the initial stop-learning sequence(“calibration”). FIG. 2 shows points on the diagram that are designatedSP_(0%) and SP_(100%). These are the positions of the actuator thatcorrespond to when the SRA 12 senses that the manipulated device reachesthe low and high end mechanical stops MSP₁ and MSP₂. FIG. 2 also shows anumber of intervals along the diagram, designated region 46 _(A)(“region A”), region 46 _(B) (“region B”), region 46 _(C) (“region C”),region 46 _(D) (“region D”) and region 46 _(E) (“region E”).

When the SRA 12 performs the calibration, it will cause the output shaft26 to rotate to determine the location of the system-defined end-stops(i.e., the mechanical stops MSP₁ and MSP₂ that limit the travel of thedevice 18). It will also determine the span of travel 20. In oneembodiment, the controller 28 is configured to make this determinationby sensing when the actual position no longer follows the commandedposition, which indicates that the manipulated device 18 has reached oneof the mechanical stops (most likely) or has otherwise encounteredfriction sufficient to stop movement (possibly due to an obstruction orother abnormality). The position of the actuator 12 when the manipulateddevice reaches the mechanical stops MSP₁ and MSP₂ is denoted as thevalues SP_(0%) and SP_(100%) respectively. The positions SP_(0%) andSP_(100%) are represented in a motor count domain (more below). Thepositions SP_(0%) and SP_(100%) also establish a working range of 100%to which the received commanded device position is mapped.

EXAMPLE

The preferred embodiment of the SRA 12 uses a BLDC type motor for motor32. It is known that this type of motor has a rotor comprised of aplurality of permanent magnets arranged axially and preferable equallyspaced on the surface of the rotor. The preferred embodiment has a motorposition sensor block 36 comprised of three Hall-effect sensors. As therotor 34 rotates, the output signal of each Hall-effect sensortransitions between two states that for the purpose of discussion arehere designated ‘1’ or ‘0’. The permanent magnets and Hall sensors areoriented such that as the rotor 34 rotates only one Hall sensor outputsignal will transition from ‘0’ to ‘1’ or from ‘1’ to ‘0’ when anytransition occurs. As the rotor 34 rotates, a certain sequence oftransitions is expected. Each transition event can be considered to be asingle motor step and since the sequence of the transitions is expected,the direction of the motor step can be determined. The amount of rotor34 rotation required to cause a step to be detected is determined by thenumber permanent magnets that form the rotor surface. The preferredembodiment uses a ten-pole rotor, five north poles and five south poles,alternately arranged. This embodiment provides that thirty Hall-statetransitions or thirty motor steps occur for every one completerevolution of the rotor 34. In other words, one motor step occurs forevery twelve degrees of rotor rotation. By keeping a count of the numberand direction of motor steps, the relative position of the motor can bedetermined.

During calibration, the non-assigned reference point along the entirerange of travel (i.e., the “center of travel” point described above) isidentified by sensor 40, and is arbitrarily assigned a position of (500)motor step counts. From there, the low-end stop is identified by thecontroller 28, by virtue of counting motor steps (i.e., countingtransitions produced by the block of Hall-Effect sensors 36) downwardfrom (500) until contact is determined, as also described above. Forpurposes of example, assume the position of the low end 0% stop is (330)motor step counts and so a value of (330) is assigned to SP_(0%).Likewise, assume the position of the high end 100% stop is determined tobe (670) motor step counts by virtue of counting transitions upward from(500) until contact is determined. The value of (670) is assigned toSP_(100%). The span is (670) minus (330), or in other words (340) motorsteps.

Before these values are established or validated, however, certaincalibration diagnostics are performed. First is limit checking. FIG. 2shows two additional points designated SP_(0%) _(—) _(LIMIT) andSP_(100%) _(—) _(LIMIT), which define the lowest and highest values(positions) that will be accepted by the stop-learning logic duringcalibration. Limit checking is performed to detect potential damage orbreakage of the coupling structure 16 or the manipulated device 18. Thefollowing criteria must be satisfied for the calibration to beconsidered valid: (1) the value for SP_(0%) must not be below SP_(0%)_(—) _(LIMIT) (i.e., not in region E); (2) the value for SP_(100%) mustnot be above SP_(100%) _(—) _(LIMIT), (i.e., not in region E); (3) thevalue for SP_(100%) must not be below SP_(0%); (4) the span (i.e.,region D) must be no less than a predetermined minimum; and (5) the span(i.e., region D) must be no greater than a predetermined maximum.Accordingly, at the end of the calibration, the values for the positionsSP_(0%) and SP_(100%) and the non-assigned reference point are loggedfor future reference.

On subsequent stop-learning sequences, these stored values are used totarget the motion of the output toward the stop. The “candidate” valuesresulting from the subsequent stop-learning sequences are compared tothe values obtained from the initial stop-learning sequence(“calibration”) and diagnostics are performed. While the SRA 12 isconfigured to dynamically update the stop-positions when it performssubsequent stop-learning sequences, there are limits. For example, toupdate the low-end stop position, any new candidate reading acquiredduring a subsequent stop-learning sequence must be within apredetermined value (“K”), plus or minus, of the initial calibrationvalue SP_(0%). This is shown in FIG. 2 and corresponds to regions A andB above and below the initial calibration for SP_(0%). The same check isperformed for the high-end stop position, and any new candidate readingacquired during a subsequent stop-learning sequence must be within apredetermined value (“K”), plus or minus, of the initial calibrationvalue SP_(100%). This is also shown in FIG. 2 and corresponds to regionsA and B. Additionally, a candidate stop position for either the low (0%)or high (100%) end that (i) falls within region E is a fatal error andwill cause the stop-learning sequence to fail as being outside thelimits and preferably results in a deactivation of the actuator; (ii)falls within region D is a non-fatal error but will cause thestop-learning sequence to fail as one involving insufficient travel; and(iii) falls within region C is a non-fatal error but will cause thestop-learning sequence to fail as one involving excessive travel.

As described in the background, in certain applications it is sufficientfor the manipulated device 18 to merely be positioned at either of themechanical stops MSP₁ and MSP₂, while in other applications it isdesirable or necessary for the manipulated device 18 to actually be heldagainst one of the mechanical stops with predetermined holding force.For example, this is desirable for an exhaust gas recirculation (EGR)valve application. The problem that arises, as also described in theBackground, is that a characteristic back electromagnetic force (BEMF)generated by the motor when rotating is not produced when not rotating(i.e., in a stall condition, as would exist when the manipulated device18 is held against a mechanical stop). Absent BEMF, only the resistanceof the motor stator coils impede current flow, and measures arenecessary to provide over-temperature protection to prevent theexcessive current from damaging either the motor or surroundingpackaging or components. Conventional approaches have involvedpositioning, without pushing, a manipulated device against the stop.However, as described above, in certain applications “close” is neitherdesirable nor adequate.

In one aspect of the invention, a method is provided for allowing theactuator 12 to distinguish between an external request to cause themanipulated device to push against one of mechanical stops, on the onehand, versus an external request to simply position the manipulateddevice at one of the mechanical stops without applying a force. Inanother aspect, a method of operating the actuator is provided, when“pushing” has been requested, so as to provide the neededover-temperature protection.

The first aspect (distinguishing “position” versus “push”) involves acouple of steps. The first step involves receiving a desired (externallycommanded) position signal (i.e., signal 24 in FIG. 1), whichincorporate a first commanded device position. In addition, a pluralityof value ranges of the first commanded device position correspond to aplurality of positioning modes of operation. Next, determining a secondcommanded device position from the first commanded device position usingthe relevant one of the plurality of positioning modes. As describedbelow, the controller 28 is configured to determine into which valuerange the first commanded device position falls into, and identify therelevant positioning mode from that determination. The next stepinvolves mapping the second commanded device position to a commandedactuator position. As described below, this mapping may be a lineartransform from the input domain (0-1000) to the detected travel span(expressed in motor counts).

Table 1 below describes in tabular form how the controller 28 isconfigured to produce the second commanded device position (i.e., withinthe range of 0-1000) using the first commanded device position.

TABLE 1 Internal Desired PWM Percent Duty Position Cycle (DC)Positioning Mode Default DC > (98%) Powered default Pos (100)positioning (1000) (96%) < DC <= (98%) Push against 100% stop (950)(95%) < DC <= (96%) Position at 100% stop without pushing Normalposition (5%) <= DC <= (95%) Normal range (50-950) positioning (50) (4%)<= DC < (5%) Position at 0% stop without pushing (0) (2%) <= DC < (4%)Push against 0% stop Default DC < (2%) Powered default Pos (100)positioning

As shown generally in Table 1, the controller 28 is configured torecognize when the first commanded position falls within one of thepredetermined value ranges as being indicative of a requested mode ofoperation (“normal mode”, “position at stop mode” or “push against stopmode”). While Table 1 reflects the logic involved in this determinationwhen the first commanded position is expressed as a duty cycle in a PWMembodiment, it should be understood that where the SRA 12 uses either ofthe UART or CAN approaches for communications, a digital informationwould itself directly define the first commanded device position, albeitin a (0-1000) range, rather than in a duty cycle percentage. Forpurposes of this description, any number in the (0-1000) range can bedivided by 10 to obtain a corresponding, equivalent percentage forpurposes of the Table 1 (e.g., a value of (30) received as digitalinformation corresponds equivalently to a 3% duty cycle under the PWMapproach). In all other respects, the description of Table 1 with regardto the PWM percent duty cycle applies equally to digital informationreceived under the UART or CAN approaches.

With continued reference to Table 1, for example, when the desiredposition signal 24 has a duty cycle of 3% (or the digital informationbeing sent has a value of (30)), then the controller 28 is configured tointerpret this as a request to “push” the manipulated device 18 againstthe low-end (0%) stop. When the signal 24 has a duty cycle of 4% (ordigital information having a value of (40)), the controller 28interprets this a request to position the device 18 at the 0% stopwithout pushing, or in other words applying a holding force against thestop. This assessment performed by the controller 28 can result in anyof the positioning modes described in Table 1.

The controller 28 will then translate the first commanded deviceposition into a second commanded device position for subsequent usebased on the relevant positioning mode. For example, when the controller28 determines that first commanded device position has a value within arange in Table 1 indicative of a normal positioning mode, then the firstcommanded device position is translated directly (without alteration)into the second commanded device position. It is the second commandeddevice position that is used in subsequent processing. Alternatively,when the controller 28 determines that the first commanded deviceposition has a value within a range in Table 1 indicative of a positionwithout pushing mode (i.e., positioning the device 18 at one of thestops without pushing), then the first commanded device position istranslated to the second commanded device position as described in theTable 1 (e.g., a suitable offset from the relevant stop, such as (50)counts, is incorporated). Further, when the controller 28 determinesthat the first commanded device position has a value within a range inTable 1 that is indicative of a “push” mode against one of the stops,then it is translated to the relevant one of the predetermined minimum(0) or maximum (1000) values, as the case may be. Additionally, as willbe described in greater detail below, the controller 28 will implementthe “push” mode by controlling the motor to position the manipulateddevice 18 against the appropriate stop while applying a motor effortthat is limited to a predetermined maximum holding effort limit.

It should be noted that the values of (1000) as a predetermined maximum,(0) as a predetermined minimum, and the various cross-over percentagesfrom one range to the next in Table 1 may be varied and remain withinthe spirit and scope of the present invention.

Once the second commanded device position, having a range between (0)and (1000), is determined using Table 1, it is then mapped to acorresponding value within an actuator position range to yield acommanded actuator position.

EXAMPLE

To extend the example previously given, the second commanded deviceposition (source) will be in the range of between (0) to (1000) and thecommanded actuator position (target) will be in the range of between(330) to (670) (in motor step counts). This may be mapped directlythrough a linear transformation, in which (50) maps to (330) and (950)maps to (670), and the intermediate values are linearly mapped. Thisequates roughly to (900) units in the source being translated to (340)units in the target, or about 3 units on the input range for every unitin the target range. Note, that values lower than (50) or higher than(950) are respectively translated to target values outside of or beyondthe learned stops. In this way, requests to push against a stop can bemade via such values lower than (50) or higher than (950). Once thisrelationship has been established, it is straightforward to translatethe second (post Table 1) commanded device position into a commandedactuator position.

FIG. 3 is a flowchart showing a method of operating an actuatoraccording to the invention. In a preferred embodiment, the actuatorposition is controlled using a proportional-integral-derivative (PID)control strategy with various compensating features. When the actuator12 is not positioning the manipulated device 18 against one of themechanical stops MSP₁ and MSP₂, the motor effort is limited by variousalgorithms being executed by controller 28 to prevent overheating of themotor coils without compromising actuator transient responsecharacteristics. However, these effort limiting means, absent thepresent invention, would not be sufficient to avoid overheating when theactuator 12 is positioning the manipulated device against a mechanicalstop for prolonged times. The present invention provides the means ofachieving the required over-temperature protection when the motor of theactuator 12 is controlled to apply a holding force against one of themechanical stops.

The method begins in steps 48 and 50, where the commanded actuatorposition (method step 48) and the present (actual) actuator position(method step 50) are provided as inputs to step 52. In step 52, thecontroller 28 determines an error amount between the commanded actuatorposition and the present actuator position. The method proceeds to step54.

In step 54, the controller 28 determines respective proportional (P),integral (I) and derivative (D) term contributions using the erroramount determined in step 52. The particular gain constants for the P, Iand D terms will vary from system to system but is well within thecapability of one of ordinary skill in the art. The method then proceedsto step 56.

In step 56, the controller 28 determines a candidate level for the drivesignal (e.g., a MPWM duty cycle) using the P, I and D contributionsdetermined in step 54, all in accordance with a predetermined controlstrategy (e.g., a PID control strategy). It should be understood thatother control strategies are known in the art, and may be selected foruse depending on the particular, transient response characteristicsdesired or required for any application. The selection of an alternatecontrol strategy (other than PID) may obviate the need to determine oneor more of the P, I and D term contributions in step 54. The candidatelevel for the drive signal 42 is one that would be provided to the drivecircuit 30 for driving the motor 32 (best shown in FIG. 1). The methodthen proceeds to step 58.

In step 58, the controller 28 determines whether a hold force limit flaghas been set. In one embodiment, two conditions that would set the flagif satisfied are as follows: (1) the first condition involves contactingthe 0% stop, where the actuator has been commanded to push against the0% stop and has in-fact reached the 0% stop, specifically (i) thecommanded actuator position is equal to or less than the 0% travel limit(i.e., corresponding to SP_(0%)) and (ii) the present actuator positionis equal to or less than the 0% travel limit (i.e., corresponding toSP_(0%)); (2) the second condition involves contacting the 100% stop,where the actuator has been commanded to push against the 100% stop andhas in-fact reached the 100% stop, specifically (i) the commandedactuator position is equal to or greater than the 100% travel limit(i.e., corresponding to SP_(100%)) and (ii) the present actuatorposition is equal to or greater than the 100% travel limit (i.e.,corresponding to SP_(100%)). If the answer to this query is YES, thenlimiting is required and the method proceeds to step 60. However, if theanswer to this query is NO, then the method branches to step 62 (thecandidate level having not been limited).

In step 60, the controller 28 is configured to limit the level of thedrive signal (in the illustrated embodiment, the duty cycle of theMPWM). The limit on the candidate level of the drive signal correspondsto a maximum holding effort (force) limit of the device against thestop. For example only, in an embodiment where the candidate level forthe drive signal (MPWM) is represented by a byte, a maximum possiblevalue would be (255), meaning that all of the available voltage (e.g.,14.4 volts in a typical automotive system) would be applied to themotor. A practical maximum may be a value of (248), since the maximumduty cycle should be less than 100%. A value of (128) may still causeexcessive current and potential damage (e.g., melting). A value for theholding effort limit may be (65), so as to ensure that excessive heat isnot generated. It should be understood that these values are exemplaryonly and may vary from application to application.

As described above, a second aspect of the invention relates to a methodfor minimizing or eliminating excessive impact of the manipulated deviceagainst either one of the mechanical stops. In this regard, andreferring again to FIG. 1, the SRA 12 is configured to effect movementfrom an initial position P₀ to a final, commanded position P₂ in twostages. The controller 28 is configured to break up this big move into afirst, relatively large move, where an intermediate position P₁ istemporarily designated as the “commanded position”, and a second,smaller move from P₁ to P₂. Given the control effect of the preferredPID controller, the first move will provide an initially large errorsignal, which will effect a rapid reduction of this error for improvedtransient response. The second move results in a relatively small errorso as to “walk” the device into the stop.

FIG. 4 is a diagram, exaggerated in scale, showing a range of travel inand around the mechanical stops. For frame of reference, the positionsP₀, P₁ and P₂ noted in FIG. 1 are carried forward to FIG. 4. Inparticular, FIG. 4 shows a region 64 surrounding the low-end (0%) stop,designated STOP_(Learned), and which, as described above, has a value,after calibration (and any subsequent learning) of SP_(0%). Region 64also contains a reference point referred to as a the low-end (0%) fixedtravel limit LIMIT_(Fixed) _(—) _(Travel) and a low-end (0%) workingstop position STOP_(Working). Likewise, FIG. 4 includes a region 66surrounding the high-end (100%) stop, designated STOP_(Learned), andwhich, as described above, has a value, after calibration (and anysubsequent learning) of SP_(100%). Region 66 also contains a high-end(100%) fixed travel limit LIMIT_(Fixed) _(—) _(Travel) and a high-end(100%) working stop position STOP_(Working). The low-end (0%) andhigh-end (100%) working stops are located a first predetermined distance(offset), in motor steps, beyond the 0% and 100% learned stop positions,respectively. The low-end (0%) and high-end (100%) fixed travel limitsare, on the other hand, located a second predetermined distance“inwards” from the 0% and 100% learned stop positions, respectively.

With continued reference to FIG. 4, when the actuator 12 is commandedfrom a position above the low-end (0%) fixed travel limit LIMIT_(Fixed)_(—) _(Travel), such as position P₀, to a position below the low-end(0%) fixed travel limit LIMIT_(Fixed) _(—) _(Travel), such as P₂, thecontroller 28 is configured for limiting the internally commandedposition (in motor steps) to the fixed travel limit LIMIT_(Fixed) _(—)_(Travel), which is at position P₁, to avoid impact at the 0% stop thatcould potentially damage the mechanism over time. Thus, between the mainposition points P₀ to P₁, the movement is characterized by a firsttransient response profile. In view of the large “error” signal betweenP₀ and P₁, the PID controller portion of controller 28 will causerelatively rapid reduction of the error—providing good transientresponse.

When the actual actuator position is below the low-end (0%) fixed travellimit, the controller 28 is configured to limit the commanded actuatorposition to a so-called moving travel limit, shown in the lower diagramof FIG. 4 as LIMIT_(Moving) _(—) _(Travel). The (0%) moving travel limitLIMIT_(Moving) _(—) _(Travel) has an initial value equal to the fixedtravel limit LIMIT_(Fixed) _(—) _(Travel). In a preferred embodiment,the low-end (0%) moving travel limit is adjusted or altered at aconstant time rate, or, in other words, by a constant value in eachsuccessive time interval, for example at points a, b, c in FIG. 4. Thecontroller 28 is configured to discontinue adjusting the low-end (0%)moving travel limit LIMIT_(Moving) _(—) _(Travel) when the low-end (0%)moving travel limit LIMIT_(Moving) _(—) _(Travel) reaches the low-end(0%) working stop position STOP_(Working). In one embodiment, thismovement of the low-end (0%) moving travel limit LIMIT_(Moving)_(—Travel) is implemented as a decrement of a predetermined value everypredetermined time period (e.g., 24 mSec intervals). The controller 28is configured, then, to continue to limit the commanded actuatorposition to the then-prevailing value of the moving travel limitLIMIT_(Moving) _(—) _(Travel). Through the foregoing, the controller 28is configured to implement a second transient response profile betweenposition P₁ to position P₂, which, in-effect, “walks” the manipulateddevice 18 into the mechanical stop.

When the commanded actuator position is changed from a position belowthe low-end (0%) learned stop position STOP_(Learned), such as positionP₂, to a position above the low-end (0%) fixed travel limitLIMIT_(Fixed) _(—) _(Travel), such as position P₀, then the controller28 is configured to reset the low-end (0%) moving travel limitLIMIT_(Moving) _(—) _(Travel) to its initial value, namely, equal to thelow-end (0%) fixed travel limit LIMIT_(Fixed) _(—) _(Travel). Once abovethe low-end (0%) fixed travel limit, the controller 28 will not limitthe commanded actuator position.

The operation of actuator 12 when in the region 66 surrounding thehigh-end (100%) stop may be substantially a minor image of the operationin the low-end (0%) region 64. It should be understood that minorvariations may be desirable or required depending on differences betweenthe 0% stop end and the 100% stop end.

When the actuator 12 is commanded from a position below the high-end(100%) fixed travel limit LIMIT_(Fixed) _(—) _(Travel) to a positionabove the high-end (100%) fixed travel limit LIMIT_(Fixed) _(—)_(Travel), the controller 28 is configured for limiting the internallycommanded position (in motor steps) to the high-end (100%) fixed travellimit LIMIT_(Fixed) _(—) _(Travel) to avoid impact at the 100% stop thatcould potentially damage the mechanism over time. This movement ischaracterized by the first transient response profile, as describedabove.

When the actual actuator position is above the high-end (100%) fixedtravel limit, the controller 28 is configured to limit the commandedactuator position to the high-end moving travel limit (not shown). The(100%) moving travel limit LIMIT_(Moving) _(—) _(Travel) has an initialvalue equal to the high-end (100%) fixed travel limit LIMIT_(Fixed) _(—)_(Travel). In a preferred embodiment, the high-end (100%) moving travellimit is adjusted or altered at a constant time rate, or, in otherwords, by a constant value in each successive time interval. Thecontroller 28 is configured to discontinue adjusting the high-end (100%)moving travel limit LIMIT_(Moving) _(—) _(Travel) when the high-end(100%) moving travel limit LIMIT_(Moving) _(—) _(Travel) reaches thehigh-end (100%) working stop position STOP_(Working). In one embodiment,this movement of the high-end (100%) moving travel limit LIMIT_(Moving)_(—) _(Travel) is implemented as an increment of a predetermined valueevery predetermined time period (e.g., 24 mSec intervals). Thecontroller 28 is configured, then, to continue to limit the commandedactuator position to the then-prevailing value of the moving travellimit LIMIT_(Moving) _(—) _(Travel). Through the foregoing, thecontroller 28 is configured to implement a second transient response,which, in-effect, “walks” the manipulated device 18 into the mechanicalstop.

When the commanded actuator position is changed from a position abovethe high-end (100%) learned stop position STOP_(Learned) to a positionbelow the high-end (100%) fixed travel limit LIMIT_(Fixed) _(—)_(Travel), then the controller 28 is configured to reset the high-end(100%) moving travel limit LIMIT_(Moving) _(—) _(Travel) to its initialvalue, namely, equal to the high-end (100%) fixed travel limitLIMIT_(Fixed) _(—) _(Travel). Once below the high-end (100%) fixedtravel limit, the controller 28 will not limit the commanded actuatorposition.

Preferably, the first aspect of the invention providing a method forlimiting the holding force against travel limit positions is used incombination with the second aspect providing a method for minimizing oreliminating excessive impact.

It should be understood that the controller 28 as described above mayinclude conventional processing apparatus known in the art, capable ofexecuting pre-programmed instructions stored in an associated memory,all performing in accordance with the functionality described herein.That is, it is contemplated that the processes described herein will beprogrammed in a preferred embodiment, with the resulting software codebeing stored in the associated memory. Implementation of the presentinvention, in software, in view of the foregoing enabling description,would require no more than routine application of programming skills byone of ordinary skill in the art. Such an electronic controller mayfurther be of the type having both ROM, RAM, a combination ofnon-volatile and volatile (modifiable) memory so that the software canbe stored and yet allow storage and processing of dynamically produceddata and/or signals.

It is to be understood that the above description is merely exemplaryrather than limiting in nature, the invention being limited only by theappended claims. Various modifications and changes may be made theretoby one of ordinary skill in the art, which embody the principles of theinvention and fall within the spirit and scope thereof.

1. A method of operating an automotive vehicle actuator having a motorcapable of overheating, wherein the motor is coupled to a manipulateddevice on the automotive vehicle, said manipulated device configured totravel through a range of motion, said range of motion limited at leastat one end by a mechanical stop, said method comprising the steps of:determining that the actuator has received a command to push themanipulated device against the mechanical stop; determining a drivesignal to be applied to the motor corresponding to a predeterminedholding force of the manipulated device against the mechanical stop,said drive signal effective to prevent overheating the motor; andapplying the drive signal to the motor so the manipulated device pushesagainst the mechanical stop with the predetermined holding force afterreaching the mechanical stop without overheating the motor.
 2. Themethod in accordance with claim 1, wherein the step of determining thatthe actuator has received a command to push the manipulated deviceagainst the mechanical stop includes the steps of receiving a commandeddevice position that is beyond the mechanical stop, and operating theactuator to move the manipulated device to a position near themechanical stop.
 3. The method in accordance with claim 1, wherein themethod further comprises the step of learning a location of themechanical stop.
 4. An automotive vehicle actuator configured to move amanipulated device on the automotive vehicle, said manipulated deviceconfigured to travel through a range of motion, said range of motionlimited at least at one end by a mechanical stop, said actuatorcomprising: a motor capable of overheating, said motor coupled to themanipulated device; and a controller configured to determine that theactuator has received a command to push the manipulated device againstthe mechanical stop, determine a drive signal to be applied to the motorcorresponding to a predetermined holding force of the manipulated deviceagainst the mechanical stop without overheating the motor, and apply thedrive signal to the motor so the manipulated device pushes against themechanical stop with the predetermined holding force after reaching themechanical stop without overheating the motor.
 5. The actuator inaccordance with claim 4, wherein the controller is further configured toreceive a commanded device position that is beyond the mechanical stop,and operate the actuator to move the manipulated device to a positionnear the mechanical stop.
 6. The actuator in accordance with claim 4,wherein the controller is further configured to learn a location of themechanical stop.